Coal drying system with trap



Nov. 29, 1955 I c. w. GORDON 2,724,904

COAL. DRYING SYSTEM WITH TRAP Fig. 2. l 3 o Nov. 29, 1955 C, W, GORDON COAL DRYING SYSTEM WITH TRAP 3 Sheets-Sheet i2 Filed Jan. 27, 1953 INVENTOR Charles W. Gordon Nov. 29, 1955 Filed Jan. 27, 1953 Percent of Collection that passes through Mesh C. W. GORDON COAL DRYING SYSTEM WITH TRAP 3 Sheets-Sheet 3 Cyclone Cyclone Mesh Fig. 4.

INVENTOR Charles W. Gordon ATTORlY Unite States Patent O COAL DRYING SYSTEM WITH TRAP Charles W. Gordon, Glen Ellyn, Ill., assigner to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Application January 27, 1953, sei-tal No. 333,508

1 Claim. (ci. 3ft- 57) My invention relates to drying systems for discrete 'material and has specific reference to such a system wherein fine coal is dried by being entrained in a stream of hot' gases and thereafter separated from said gases by means of a cyclone separator.

In conventional drying .systems of this type where ordinances prohibit contamination of the air with coal dust or so called ultra fines the exhaust gases leaving the large cyclone separator are cleaned by being passed through a wet scrubber. Since the disposition of the wet sludge formed in the scrubber is a very considerable problem, a very small cyclone .separator is employed intermediate the scrubber and the large cyclone which is effective to separate a large portion of this dust in the exhaust gases before they enter the scrubber. While this arrangement is very effective in cleaning the air the use of two cyclone separators results in a high power consumption and consequently rather high operating costs.

Also in conventional systems of this type wherein the coal being dried is relatively soft it has been found that a large percentage of the coarse fractions of the coal were reduced to an undesirably small size due to the attrition of the coal passing through the cyclone. Since it is essential that coal particles be a predetermined minimum size in order to be salable this effect of the cyclone separator has resulted in a substantial waste of coal as well as a financial loss to those employing' such systems.

It is the general object of my invention to provide an improved coal drying system employing a cyclone separator wherein the reduction in size in the coarse coal fractions is substantially eliminated and wherein the employment of additional cyclone separators is unnecessary.

A more specific object is to provide an improved coal drying system employing a cyclone separator with a trap immediately adjacent the inlet of said separator effective to separate a substantial portion of the coarse coal fractions prior to their entry into said separator.

Other and further objects of my invention will become apparent to those skilled in the art as the description proceeds.

Withthe aforementionedy objects in View, my invention comprisesfan arrangement, construction and combination of the elements of the drying system in such a manner as to attain the results desired as hereafter more particularly set forth in the following detailed description of an illustrative embodiment said embodiment being shown by the accompanying drawings wherein:

Figure l is a diagrammatic side elevation of a coal drying system embodying my invention.

Figure 2 is a transverse sectional View through the trap taken generally along line 2 2 of Fig. l.

Figure 3 is a perspective View of the upper portion of the trap taken from below the pivotal damper actuating mechanism looking upward.

Figure 4 represents a set of curves plotted from actual tests and shows the results obtained with a conventional 2,724,904 Patented Nov. 29, 1955 ICC 2 installation and an installation having my invention incorporated therein. l l

Referring now to the drawings the coal drying system of Fig. 1 comprises a drying column 10 communicating at its inlet end with a suitable furnace 12 and at 'its outlet end with gravity separation chamber or trap 14. Hot gases, either hot air or combustion gases, are generated in furnace 12 and conveyed through conduit 16 to column 10 through which they ow upwardly to trap 14.

A mixture of wet and dry coal is introduced into the drying column 10 through feeder-mixer 18 and is conveyed upwardly through said drying column by the stream of hot gases. These hot gases dry the coal during its ascent through said drying column and upon leaving the outlet of said column convey the now dry coal through trap 14 into the cyclone separator 20. The hot gases are drawn through the top of the cyclone separator by fan 19 and exhausted through conduitZZ while the coal that is separated from the gases in the cyclone passes through air lock valve 24 located at the bottom of the cyclone. The dry coal passing through valve 24 is conveyed downwardly through conduit 26 to a point of use with a controlled portion of this dried coal being diverted by valve 28 through conduit 30 into feeder-mixer 18 for mixing with the wet coal introduced into said feeder-mixer by endless conveyor 32.

The previously mentioned trap 14 is of rectangular section (Fig. 2) and is provided with a tapered bottom portion for collection of the relative coarse fractions of coal that are separated from the gases flowing through the trap. The bottom of this trap is provided with an air lock valve 34 similar to valve 24 and through which the coarse coal fractions are continuously discharged. To substantially reduce the velocity of ow through the trap relative to that of the drying column 10 the transverse sectio'n 'of the trap relative to the direction of flow therethrough is considerably larger than that of the drying column.

In order to control the flow pattern through trap 14 adjustable baille 35 and pivotally mounted damper 37 are provided within said trap.

Bale 3S comprises a vertically disposed rectangular plate inserted through slot 39 in the top of trap 14 and is provided with a series of vertically spaced holes 41 through which retaining rod 43 is inserted to adjustably limit the distance that said baffle depends into the interior of the trap.

The damper 37 is mounted upon shaft 45 adjacent the outlet of the trap and isy adjustable between the extreme positions indicated by the dotted lines in Fig. 1. The adjustment of the damper 37 is accomplished through arms 47 pivotally connected to the damper. The outer ends of said arms are provided with transversely formed teeth operatively engaged by complementary teeth of pinions 49. Saidl pinions are secured to shaft 51 which is jour'- naled in support members S3 secured to the adjacent wall of trap' 14 and which is provided with a suitable hand- Wheel 55. A stud 57 is` threadedly received within a suitable opening formed in a portion of support member 53 and may be moved into' engagement Awith the teeth of pinion 49' to retain the' damper ir any desired adjusted position within its predetermined limits.

In operation, the hot gases generated by furnace 12, pass upwardly through drying column 10 carrying with them the mixture of wet and dry coal introduced into said drying column by feeder-mixer 18. The coal upon reach ing trap 14 is almost completely dry and upon passing through said trap the velocity of the coal and gas mixture is substantially reduced due to the greater sectional area of the trap. The coarse fractions under the inuence of gravity settle to the bottom of the trap while the less coarse or ner fractions remain entrained in the stream of gases and pass through the outlet of the trap into cyclone 20. Within said cyclone a substantially complete separation of the coal and hot gases is accomplished with the hot gases passing through the top thereof and the coal particles passing outwardly through the f bottom.

In a system of this kind it has been found necessary to control within limits the distribution of coal between the trap and the cyclone, i. e., the percentage of total separation that takes place within trap 14. In the illustrative and preferred embodiment this control is brought about by changing the pattern of flow of the coal and hot gases through said trap by means of bale 35 and damper 37. With these ow obstructing elements it has been possible to vary the percentage of total separation within trap 14 from approximately 27% to better than 80% with maximum separation being had when these elements are in their extreme ilow obstructing position thereby effectively lengthening the ow path through trap 14.

By separating the coarse fractions of the coal in trap 14 prior to their entry into cyclone separator 24 these coal particles are not subjected to the abrasive effect of the centrifugal separation produced by cyclone separator 20. Said particles of coal therefore are not reduced in size to any substantial extent but are removed from the drying system in substantially the same condition in which they entered said system except that a majority of the moisture has been removed therefrom.

The fact that my novel system substantially eliminates degradation of the coal is clearly evident from a consideration of the curves set out in Fig. 4, which are plotted from test results obtained from a full sized installation and represent percentages of various collections that will pass through a particular mesh. The abscissa of the curve sheet is divided so as to represent the mesh of a screen and the ordinate so as to represent percentage of material that passes through the screen.

The curve represented by the dotted line labeled cyclone indicates results obtained with the collection from a conventional system, i. e., a system Without the trap, and the curves represented by solid lines and labeled trap and cyclone indicate results obtained with the trap and cyclone collections, respectively, from my novel system. The curve labeled feed represents results obtained with the material fed to both systems, which feed was identical.

The conditions under which the tests were made were identical for both systems and in my novel system about 80% of the total collection was in the trap and 20% in the cyclone.

In analyzing these curves it will be noted that the curve representing the conventional system is considerably below the curve for the feed, this variation indicating the amount of degradation produced in such a system. In contrast to this, the composite of the trap and cyclone curves for my novel system practically coincides with the feed curve (the trap curve representing 80% of total collection and the cyclone curve 20%) indicating that no overall degradation takes place with this system. Moreover, the curves for my novel system indicate that this system produces a successful classification of the coal without the use of other classifying means such as screens, since the product discharged from the trap is coarser than the incoming feed.

With this organization it is thus possible to use the well known and highly efficient drying systems employing upstanding drying columns and centrifugal separators without rendering a large percentage of the coal unsalable by so reducing it in size that it cannot be marketed. Furthermore, the cyclone separator employed with my novel system can be made very small as compared with the separators of conventional systems since a majority of the material is separated in the trap. This eliminates the need for the two cyclones formerly needed Where air contamination is prohibited and in such instances results in a more eiciently operating unit.

While I have illustrated and described a preferred embodiment of my novel drying system it is to be understood that such is merely illustrative and not restrictive and that variations and moditications'may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of my invention.

What I claim is:

A drying system for discrete coal comprising a generally upright drying column adapted to have said material passed upwardly therethrough entrained in a stream of hot gases, a gravity separation chamber having a substantially horizontal roof and a hopper bottom, said chamber being provided with a vertically elongated inlet opening extending downward from the roof and an outlet opening in its upper portion directly opposite said inlet opening, said inlet opening communicating with the interior of the drying column through an elongated opening provided in the side wall of the upper end of said column, said chamber having a cross section relative to the general direction of the ow of material and gases therethrough substantially larger than that of the drying column, means for regulating the flow pattern through said chamber including a damper effective to controllably restrict said outlet mounted for pivotal movement about an axis extending transversely across the lower edge of the outlet, means to adjustably position said damper about its pivotal axis, a vertically disposed baille plate extending downward from the roof of the chamber and across the chamber relative to the direction of ow therethrough, said bafe plate being disposed slightly upstream of the leading edge of the damper, means for adjusting the vertical distance that the baffle plate depends into the chamber, and a cyclone separator connected with the outlet of said chamber to receive the hot gases from said chamber together with the portion of the material remaining entrained therein to substantially completely separate said material and gases.

References Cited in the le of this patent UNITED STATES PATENTS 748,893 Trump Ian. 5, 1904 1,024,297 Thompson Apr. 23, 1912 1,766,030 Meakin June 24, 1930 2,047,568 Lissman Iuly 14, 1936 2,296,159 Gordon Sept. 15, 1942 2,313,956 McGrane Mar. 16, 1943 FOREIGN PATENTS 215,812 Great Britain May 19, 1924 

